1. Field of the Invention
The present invention relates generally to cryogenic cooling systems, and, more particularly, to such cooling systems especially useful in environments where weight and space requirements are at a premium.
2. Description of Related Art
There are an increasing number of devices which for proper operation require cooling to very low temperatures. For example, certain infrared detectors used in heat seeking missile guidance systems require cryogenic cooling.
In the past where such cryogenic cooling was needed on board a missile, for example, the cooling could only be satisfied by the use of a cryosystem which added an excessive amount of weight. For example, conventional on-board cryosystems typically consisted of Joule-Thomson gas liquifying cryostats, stored high pressure gas bottles, and control and pressure regulating valves, which added weight generally in excess of one pound, and additional cost to the missile vehicle. The weight from such a system is prohibitively large for some missile system requirements.
Another past approach has been to provide a mechanical closed-cycle refrigerator such as a split-Stirling cryoengine having a weight of several pounds, making it even less desirable from the weight standpoint.
Still other types of cooling systems used in space satellite vehicles have used solid cryogen coolers. These have generally been very large in size to provide cooling over many months duration while in space. In these cooling systems, the solid cryogen is frozen in place, or inserted as a prefrozen slug, just prior to launching the vehicle into space. Cooling is achieved by virtue of the latent heat of sublimation achieved by sublimating the solid cryogen into space vacuum. Such systems are for one-shot use only and also require that the cryogen vapor venting be pressure controlled.
Adequate external coolant is generally available on the missile launcher or launch platform to cool down the infrared detector and to maintain its operation in a standby mode prior to missile launch. It is, therefore, highly desirable to be able to provide a cryogenic system for airborne vehicles, such as missiles, for example, which would provide cooling for launch readiness through the use of an external precoolant and that would maintain the cooling with a very small solid cryogen phase change cooler placed next to the infrared detector, without the need to supply cryogen continuously during missile flight, as is the case with gas fed Joule-Thomson cryocoolers or a closed cycle mechanical refrigerator.